The invention relates to the testing of electrical loads, such as appliances, connected with a DC supply in a motor vehicle and which are adapted to receive control signals from an electronic control unit which is adapted to be connected with a diagnostic computer, for instance via an interface adapter, so that testing may be performed by running test software in the computer, stored for instance on a diskette.
The invention takes as a starting point a diagnostic system for road vehicles as described in the standard specification DIN/ISO 9141, dated September 1987. This standard specifies the requirements for an exchange of digital information between electronic control units of motor vehicles and diagnostic testing equipment. This exchange of information is intended to facilitate the checking, testing, diagnosis and adjustment of vehicles, systems and electronic control units. FIG. 1 of the standard (shown in FIG. 1 herein) shows in this connection the relevant features of a vehicle, while FIG. 2 on the other hand shows the respective diagnostic unit. In FIG. 1 the vehicle is denoted by a dotted outline 1. To the extent that they are relevant for the present purpose the parts of the electrical system of the vehicle are: the battery 2, constituting the power source to supply the electrical loads such as drive motors, servo motors, electromagnets, actuators and the like denoted generally by 15, the measuring and detecting means generally denoted 14 and the electronic control unit ECU. The latter receives signals from the sensors 14 via wires 3. The loads of appliances 15 receive their control signals from the electronic control unit ECU via suitable control lines 4.
The electronic control unit ECU is furthermore connected with the DC supply 2 via suitable power lines 5 and 6. In the power line 6 a replaceable fuse 7 is connected to protect the main power line. Furthermore to comply with the said standard DIN/ISO 9141 the electronic control unit ECU has either only one single communication connection K or two communication connections K and L which make it possible to establish the diagnostic or testing connection with the diagnostic unit 8 and 16 for the testing routine. The main parts of the diagnostic unit are the diagnostic computer 16, which may be in the form of a computer already present in the workshop as more or less standard equipment, such as a personal computer, or device which may be carried for place to place by the test staff, which, in accordance with the specific application, is able to be connected using one communication line (K), or two lines (K) and (L), or, if the electronic control unit ECU and the diagnostic computer 16 are not part of the same data transmission system, with an interface adapter 8 with a serial interface 9 (as for instance an RS 232 interface). It is stated in paragraph 4.1 of the said standard DIN/ISO that electronic control units have to have one or two communication connections (K) or, respectively, (K) and (L) for checking the testing operation and the diagnosis. Furthermore it is necessary for the battery voltage and the common return line for the diagnostic device have to be able either on the electronic control unit ECU or on the vehicle 1. If the lines K and L of two or more electronic control units ECUs are connected together, the resulting system is termed a bus system. The line K is defined as the like, which transmits the information in a digital and serial form from the electronic control unit ECU to the diagnostic computer 16. The line K may also be used bidirectionally; in this case it may also transmit control signals or data from the diagnostic computer 16 to the electronic control unit ECU. The line K may also be used to initialize serial communication. The line L is defined as the unidirectional line from the diagnostic computer 16 to the electronic control unit ECU. If the latter is present if may be used to initialize the serial communication and/or to transmit control signals or data or both. It will be seen from this account that the line K may be either unidirectional or bidirectional and the line L may be omitted, so that it is only possible to have the following four configurations:
1 A bidirectional line K with a unidirectional line L.
2 a unidirectional line K with a unidirectional line L
3 A bidirectional line K without any line L.
4 A unidirectional line K without any line L.
In each of the four cases it is possible to initialize in some other way, that is to say as an alternative to the use of the lines K and L. Page 4 of the said Standard DIN/ISO 9141 shows various configurations of the systems and gives details regarding on the function of the communication lines K and L. Chapter 4.2 (page 5) shows the principle of a setup for testing.
Although this standardization of the testing and diagnostic procedures, of the devices for use therein and the adaptations of the vehicles meet normal requirements there is one problem in connection with the structure and function of the electronic control unit ECU: although on the basis of the existing hardware and installed software such an electronic control unit to perform a selftest with a non-volatile storage of the fault and to check the frequency of the fault, the electronic control unit is not in a position of ascertaining the electrical power requirements of the individual electrical loads or appliances 15. That is to say, the electronic control unit is only able check the operational or nonoperational condition of the electrical appliances on the basis of two possible states without any intermediate values. However, specific information about the "quality" or "size" of a defect in the respective electrical load which would be extremely helpful to make a systematic and expert repair to the unit concerned.